The rated capacity must not be greater than 87% of the hydraulic capacity at maximum reach/radius. However when calculating the rated capacity there are two key machine features that must be considered – stability and hydraulic capacity. This includes the speed of operation, the applied load, the length of each rope or line, size, number, and etc. To come up with a WLL or MRC value, there are many factors to consider. It’s the responsibility of the manufacturer to determine the right or approximate MRC value for each hoisting device. When used on a crane, hoist or winch the Rated Capacity includes the weight of any attachments, spreader beams or lifting devices below the crane hook and is the maximum allowable lifting capacity of the crane, hoist or winch when the lift is a straight line pull. For example, the rated capacity for an excavator, is maximum load that can be lifted over side at full reach on the maximum allowable slope. MRC is often called the Manufacturers Rated Capacity or Maximum Rated Capacity (MRC) to avoid any confusion with maximum gross load. The definition of Rated Capacity is the maximum gross load which may be applied to the crane or hoist or lifting attachment while in a particular working configuration and under a particular condition of use. In the preface of AS1418.1 the following insight is provided into the change – “The term ‘safe working load’ has been changed to ‘rated capacity’ and other uses of the word ‘safe’ have been avoided due to the legal significance placed on the word.” SO WHAT DOES THAT DEFINITION REALLY MEAN? Any reference to the acronym ‘ SWL’ was removed from the Standard and replaced with “rated capacity”. The Australian Standard 1418.1 Cranes, Hoists and Winches was revised in 2002 and one of the key changes related to this terminology. Lifting capacity labelling is an important component of a safe system of work, and the most significant change to the assessment of lifting capacity occurred over a decade ago with the replacement of ‘Safe Working Load’ to ‘Rated Capacity’. The lifting of any freely suspended load, is a high risk activity requiring a range of controls to ensure work is performed safely.
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